Exponential resistance material and method of manufacturing same

ABSTRACT

A voltage drop across a resistance element, wherein the resistance varies exponentially with the voltage, is expressed by the equation: E B X I1/n WHEREIN I is the current through the element, B is a constant and is equal to the voltage value at which the current through the element is equal to 1 Ampere, and E is the voltage drop. To achieve a variable B-value based on the resistance material itself and furthermore to achieve a greater dependence of the resistance on the voltage drop, the value of n can be selectively raised by varying the composition of the resistance element as follows: 50 - 90% ZnO 0.1 - 40% ZnF2 0.1 - 40% MeO wherein MeO is an oxide selected from the oxides of magnesium, calcium, strontium, barium, iron, cobalt, lead, boron, aluminum, bismuth, manganese, chromium, nickel, antimony, and mixtures thereof. An improved method of manufacturing such a resistance material is also described.

United States Patent 91 Lauterbach-Dammler EXPONENTIAL RESISTANCEMATERIAL AND METHOD OF MANUFACTURING SAME [75] Inventor: IngeLauterbach-Dammler,

[30] Foreign Application Priority Data July 18, 1973 Germany .t 2336504[52] US. Cl. 252/519; 252/518; 252/520; 264/61; 264/67; 264/104 [51]Int. Cl. 01B 1/08 [53] Field of Search 252/518-521; 264/67, 61, 104

[56] References Cited UNITED STATES PATENTS 3,642,664 2/1972 Masuyama eta1 252/519 3,658,725 4/1972 Masuyama et a1 .t 252/519 X PrimaryExaminer-Benjamin R. Padgett Assistant Examiner-E. Suzanne ParrAttorney, Agent, or Firm-Gifford, Chandler & Sheridan 1 Dec. 9, 1975 [57ABSTRACT A voltage drop across a resistance element, wherein theresistance varies exponentially with the voltage, is expressed by theequation:

E a x 1" wherein I is the current through the element, B is a constantand is equal to the voltage value at which the current through theelement is equal to l Ampere, and E is the voltage drop. To achieve avariable B-value based on the resistance material itself and furthermoreto achieve a greater dependence of the resistance on the voltage drop,the value of n can be selectively raised by varying the composition ofthe resistance element as follows:

50 90% ZnO 0.1 40% ZnF 0.1 40% MeO wherein MeO is an oxide selected fromthe oxides of magnesium, calcium, strontium, barium, iron, cobalt, lead,boron, aluminum, bismuth, manganese, chr0- mium, nickel, antimony, andmixtures thereof. An improved method of manufacturing such a resistancematerial is also described.

10 Claims, No Drawings EXPONENTIAL RESISTANCE MATERIAL AND METHOD OFMANUFACTURING SAME BACKGROUND OF THE INVENTION The invention relates toa resistance material wherein the resistance varies exponentially withthe voltage drop and, more particularly, relates to a sinteredceterminal wires (pigtails) can be attached.

ramic material for non-linear resistance elements. The

invention also relates to a method of manufacturing such material.

Such resistance materials are well known and have been made from, forexample, silicon carbide, titanium dioxide or zinc oxide. The voltagedrop across elements made from such materials is given by the followingequation:

wherein E is the voltage drop over the element, I is the current flowingthrough the element, and B is a constant reflecting the voltage value atcurrent I 1 Ampere. The exponent n is, therefore, a direct measure ofthe magnitude of non-linearity based on p-n-transitions, on the contactamong the individual grains, or on the material itself.

It is known that the B-value of a non-linear resistance element may bevaried by sintering at varying temperatures and under differentatmospheres. It is further known to adjust the B-value through thethickness of the resistance elements. Both procedures permit only alimited possibility of variation. Thus, when there is a change intemperature the desired n-value, in many cases, is not attained and whenthere is a change in thickness, desired small increments of resistanceoften are not attainable.

DESCRIPTION OF THE INVENTION It is therefore an object underlying theinvention to provide a composition wherein the electrical resistance isgreatly dependent on voltage and thus has a large nvalue anda variableB-value based on the material itself.

It is a further object to provide a method of manufacturing such acomposition.

The first object is particularly advantageously solved by a compositioncomprising about 50-90% ZnO, about 0.1 40% ZnF and about 0.1 40% MeO;wherein MeO is an oxide selected from the oxides of magnesium, calcium,strontium, barium, iron, cobalt, lead, boron, aluminum, bismuth,manganese, chromium, nickel, antimony, and mixtures thereof. Accordingto the invention, the B-value of the material may be varied within wideranges by changing the ratio of the two components ZnO and ZnF,. If,meanwhile, the metal oxide content is kept unchanged, the n-value of thematerial remains nearly constant. However the nvalue can be adjusted tomany values by varying the MeO content.

The following Examples and the Table explain in more detail therelationship of the electric properties of the compositions of theinvention and the method of manufacture of the compositions.

EXAMPLE 1 Two mole each of Bi O C0 0,, MnO, and Sb O (a preferredcomposition) were homogeneously mixed with varying amounts of ZnO andZnF After a presintering at 600C the material was ground, compacted toAs can be seen from the values in Table l, the B- value increases nearlylinearly with increasing ZnF content, whereas the n-value of 20 to 25remains nearly constant.

EXAMPLE 2 Three mole of each of Bi.,o,, C0 0 Mn0 and Sb O werehomogeneously mixed together with varying amounts of ZnO and ZnF andwere further processed according to the procedure described in Examplel.

The electrical values of the resulting element are listed in Table 1(numbers 7-9). A comparison with Examples 1 to 6 shows that a smallchange in the metal oxide content effects a considerable change in thenvalue.

Repetition of the fore going examples with a wide variety ofcompositions having difiering ZnO to ZnF, ratios and difieringproportions of the oxides of the invention established that theadvantages of the invention were attained when the ZnO was in the rangeof about 50-90%, the ZnF, was in the range of about 0.1 40%, and the MeOwas in the range of about 0.1 40%. Further, the composition was found tobe particularly useful when the ZnF content was about 1-8% and the MeOcontent was about 2-l6%.

Similarly, repetition of the above examples with presintering at varioustemperatures and annealing the formed element at various temperaturesshowed that the best forming conditions for the resistance mate rial waspresintering at about 600900C and annealing at about lO00-l400C.

It is, of course, to be understood that the present invention is notlimited to the specific examples given, but also comprises anymodifications within the scope of the appended claims.

I claim:

1. A composition adapted for use as an electrical resistance elementwherein the electrical resistance varies exponentially with the voltagedrop across the elementksaigl vp ltage drop being given by the equation:

X I wherein E is said voltage drop; I is the current through theelement, B is a constant equal to the voltagevalue at which the currentis equal to l Ampere, and n is a number; said composition comprisingabout 50-90% ZnO, about 0.1 40% ZnF and about 0.1 40% MeO; wherein MeOis an oxide selected from the oxides of magnesium, calcium, strontium,barium, iron, cobalt, lead, boron, aluminum, bismuth, manganese,chromium, nickel, antimony, and mixtures thereof.

2. The composition according to claim 1 in which the ZnF proportion isabout l8% and the MeO content is about 246%.

3. The composition according to claim 1 wherein said MeO isapproximately equal molar proportions of Bizoa, C030, Mnoz, and Sb203.

4. The composition according to claim 2 wherein said MeO isapproximately equal molar proportions of Bigoa, C0304, M1102, and sbgoa.

5. The composition according to claim 1 wherein said composition is inthe form of a resistance element.

6. The method of manufacturing a composition adaptable for use as anelectrical resistance element which method comprises the steps of a.forming a homogeneous mixture of about 50-90% ZnO, about 0.1 40% ZnF andabout 0.1 40% MeO wherein MeO is an oxide selected from the oxides ofmagnesium, calcium, strontium, barium, iron, cobalt, lead, boron,aluminum, bismuth, manganese, chronium, nickel, antimony, and mixturesthereof;

b. sintering said mixture at about 600-900C.;

c. grinding the sintered mixture;

d. compacting the resulting mixture; and

e. annealing the resulting material at about 1000 7. The methodaccording to claim 6 wherein said ground mixture is compacted to theform of a resistance element.

8. The method according to claim 6 wherein said MeO is approximatelyequal molar proportions of Blzoa, C0304, Mnoz, and Sb203.

9. The method according to claim 7 wherein said MeO is approximatelyequal molar proportions of Bi o C0 0 Mno and Sb O 10. The methodaccording to claim 6 and further comprising the step of positioningmetal electrical contacts on portions of said resistance element.

1. A COMPOSITION ADAPTED FOR USE AS AN ELECTRICAL RESISTANCE ELEMENTWHEREIN THE ELECTRICAL RESISTANCE VERIES EXPONENTIALLY WITH THE VOLTAGEDROP ACROSS THE ELEMENT, SAID VOLTAGE DROP BEING GIVEN BY THE EQUATION:2. The composition according to claim 1 in which the ZnF2 proportion isabout 1-8% and the MeO content is about 2-16%.
 3. The compositionaccording to claim 1 wherein said MeO is approximately equal molarproportions of Bi2O3, Co3O4, MnO2, and Sb2O3.
 4. The compositionaccording to claim 2 wherein said MeO is approximately equal molarproportions of Bi2O3, Co3O4, MnO2, and Sb2O3.
 5. The compositionaccording to claim 1 wherein said composition is in the form of aresistance element.
 6. The method of manufacturing a compositionadaptable for use as an electrical resistance element which methodcomprises the steps of a. forming a homogeneous mixture of about 50-90%ZnO, about 0.1 - 40% ZnF2, and about 0.1 - 40% MeO wherein MeO is anoxide selected from the oxides of magnesium, calcium, strontium, barium,iron, cobalt, lead, boron, aluminum, bismuth, manganese, chronium,nickel, antimony, and mixtures thereof; b. sintering said mixture atabout 600*-900*C.; c. grinding the sintered mixture; d. compacting theresulting mixture; and e. annealing the resulting material at about1000* - 1400*C.
 7. The method according to claim 6 wherein said groundmixture is compacted to the form of a resistance element.
 8. The methodaccording to claim 6 wherein said MeO is approximately equal molarproportions of Bi2O3, Co3O4, MnO2, and Sb2O3.
 9. The method according toclaim 7 wherein said MeO is approximately equal molar proportions ofBi2O3, Co3O4, MnO2, and Sb2O3.
 10. The method according to claim 6 andfurther comprising the step of positioning metal electrical contacts onportions of said resistance element.